Glass substrate coated with thin multifilms for protection against solar radiation

ABSTRACT

Glass composites, containing a glass substrate (1) on which is deposited an underlying film (2) based on tantalum oxide, titanium oxide or tin oxide, on which is deposited a functional film (3) based on an alloy of chromium and nickel or based on tantalum, on which is deposited an overlying film (4) based on titanium oxide, titanium nitride or tantalum oxide, provide effective protection against solar radiation while exhibiting excellent wear and corrosion resistance.

This is a Continuation, of application Ser. No. 08/251,285, filed on May31, 1994, now U.S. Pat. No. 573,831, Continuation of application Ser.No. 07/875,815, filed on Apr. 30, 1992, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to glazing panes for thermal insulationand/or protection against solar radiation, and more especially a glasssubstrate provided with functional thin films deposited under vacuum.

2. Discussion of the Background

Substrates having multifilms are useful as glass equipment for buildingsor ships. In fact, by affecting the amount of energy of the solarradiation transmitted, excessive heating inside rooms, which inespecially uncomfortable in summer, may be avoided, and thus the energyconsumption required for the air conditioning of said rooms may belimited. This point is especially crucial in that the present-daytendency is to increase the proportion of the glazed areas on thefacades of buildings.

There exist, however, other requirements which make such substrateshaving films very suitable for use in buildings, a primary requirementbeing the durability of the thin films, especially where the glazingpanes are intended for use as monolithic glazing.

It is, in fact, important for this substrate coated with thin films tobe suitable for use in monolithic glazing. This application implies thatthe thin films shall be wear-resistant over time, even without beingprotected an they would be in the interior of a laminated pane or amultiple glazing pane of the double glazing type. Now in a monolithicglazing, the thin films are directly subject to attack both of amechanical nature, for example by friction creating scratches andleading to defects in appearance in transmission as well as inreflection, and to attack of a chemical nature, for example on contactwith humidity and/or pollution of the surrounding atmosphere or when thepane is cleaned with chemical products.

Nor must a requirement of an aesthetic nature be forgotten; it isdesirable that the glazings when viewed in external reflections shall beable to exhibit varying tints notably rather soft and pastel shades.

It is not usually necessary to have, for building construction, paneshaving a very high transmission of light as may be the case for anautomobile, for example for windshields, but it is neverthelessadvantageous to be able to offer types of glazing having differentlevels of light transmission.

With regard to the method of producing the thin films, the techniques ofdeposition under vacuum, notably using cathodic sputtering, are wellknown and enable the optical performances of the films obtained to bewell controlled. In particular, those techniques are known which arecarried out in the presence of a magnetic field, which multiplies theimpacts of the ions on the target and accelerates the deposition.Mention may be made, for example, of Pat. DE-24 63 431 C2, whichpresents such a method using a planar magnetron, and of the U.S. Pat.No. 4,116,806, which utilizes a target in the form of a belt, known as a"belt track".

Similarly, reactive cathodic sputtering techniques are known, whichenable a thin film to be produced by causing the material of the targetto react with a gas of the plasma; U.S. Pat. No. 3,907,660 thus presentssuch a method for the deposition of metallic oxide on glass.

Among the thin metallic or other films acting upon solar radiation,notably by reducing the energy transmission, T_(E), both by absorptionand by reflection, films based upon a chrome-nickel alloy oriron-chrome-nickel alloy are known. Thus, U.S. Pat. No. 4,022,947presents more especially a substrate of glass provided with a film madefrom one of these alloys and a film of the oxide corresponding to saidalloy. This oxide film is placed either on the functional film, itselfdeposited onto the substrate, or between the substrate and saidfunctional film. In the former case, it has an essentially protectiverole, but without this protection being calculated. In the latter case,it has an essentially interferential role for the purpose of modifyingthe coloration on the glass side, but without the intensity thereofbeing indicated.

Thus, there remains a need for glass panes which are coated with thinfilms which can control the amount of energy transmission of solarradiation.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide novelglass substrates having coated thereon thin multifilms, whicheffectively fulfil a protective function against solar radiation, arehighly resistant both mechanically and chemically on the film side, andoffer a range of varied colorations and purities of tint in reflectionon the glass side.

It is another object to provide a method for protecting against solarradiation by installing such a glass composite in a building or ship.

These and other objects, which will become apparent during the followingdetailed description, have been achieved by the inventors' discoverythat glass composites, comprising a glass substrate having thinmultifilms comprising a functional film either of metallic alloy basedon chromium and nickel or based on tantalum deposited on a film based ontantalum oxide, titanium oxide, or tin oxide and covered by a film of ametallic compound such as titanium oxide or titanium nitride or tantalumoxide offer good protection against solar radiation.

BRIEF DESCRIPTION OF THE DRAWING

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same become betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawing, wherein:

FIG. 1 is a simplified sectional view through a glass substrate havingthin films according to the present invention. For reasons of clarity,the thickness ratios have not been drawn to scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Thus, the present glass composites comprise a glass substrate on whichis coated an underlying film, on which is coated a functional film, onwhich is coated an overlying film. Suitable substrates include any glasswhich is suitable for use as a glass pane in, e.g., a building or ship.Typically, the glass pane is flat, and silico-sodo-calcic glasses arepreferred. The thickness of the glass substrate is not critical but isgenerally from 1 to 20 mm, preferably from 2 to 10 mm.

According to the present invention, the glass composite comprises afunctional film of essentially metallic alloy based upon chromium andnickel. Apart from these two metals, the alloy may contain also iron,and thus belong to the family of the stainless steels (such an steel 316L, according to A.I.S.I. standard). Such alloys are disclosed in U.S.Pat. No. 4,022,947, which is incorporated herein by reference.Preferably, said alloy is nitrided, which gives it a greater mechanicalstrength. Such nitrided alloys are preferably prepared by employing anatmosphere which is completely nitrogen during the formation of thefunctional film. Its thickness may vary and is preferably less than 100nm and notably between 10 and 100 nm. In fact, it is this film whichgives to the final pane its solar radiation protection properties, byreducing the value of T_(E). Another functional film according to thepresent invention is based upon tantalum, the thickness of which ismodulated according to the desired light transmission.

It should be noted that with this type of film it is impossible to actupon the factor T_(E) without also acting upon the light transmissionfactor, T_(L), where more than 50% of the solar energy lies in thewavelength range between 0.38 and 0.78 nm, that is to say within thevisible range. This leads, depending upon the thickness of the alloyfilm used, to proposing glazing panes having different "couples" of thevalue T_(L) and T_(E), each corresponding to a judicious compromisebetween a sufficient visibility in transmission and an acceptablethermal comfort, if only as a function of the latitude of the countriesfor which the final glazings are intended. The thicknesses generallyremain, however, less than 100 nm.

With advantage, an alloy based upon nickel-chromium will be used,because it is easy to process and moderate in cost. This type of alloyis furthermore easy to use because its deposition by cathodic sputteringcan be carried out at a high rate. Its characteristics are alsoadvantageous in that it has good performances and notably an improvedemissivity. The conjugate presence of nickel and chromium also leads toan appearance in reflection of the glazing on the side carrying thefilms which is pleasant to the eye. The ratio by mass of nickel tochromium is preferably of the order of 70/30 to 30/70, most preferablyabout 55/45, in the case where the alloy contains essentially nickel andchromium.

The film based upon metal and/or metallic compounds according(functional film) to this invention is placed on a metallic oxide filmwhich will be designated hereinafter as the "underlying film" and which,itself, is deposited directly on the glass substrate. The film basedupon metal and/or metallic compounds (functional film) is, furthermore,coated with another film of metallic compound, which will hereinafter bedesignated by the term "overlying film".

The underlying film is advantageously based upon tantalum oxide, Ta₂ O₅,tin oxide, SnO₂, or titanium oxide TiO₂, and its thickness is from 10 to220 nm, preferably 12 to 150 nm, most preferably 12 to 120 nm. It has athreefold function: apart from the fact that it promotes adhesion of thefunctional film to the substrate, its appreciable thickness gives it aninterferential function for acting upon the appearance in lightreflection of the glazing, but also a primary function with regard tothe physico-chemical resistance of the whole stack of films.Surprisingly, in fact, the inventors of the present invention havedemonstrated, as shown in the examples given below, the fact that thenature of the underlying film is not without effect in regard to thebehavior under attack, notably of a chemical nature, of the stack offilms.

Thus, if the underlying film is not suitably chosen, chemical corrosionmay appear at the level of the underlying film, and more especially atthe glass/underlying film interface, said corrosion leading to thelocalized destruction of the underlying film and for this reason leadingto detachment of the outer layers. Now the oxides chosen for theunderlying film are very advantageously especially chemically resistantboth to humidity and to pollution and are therefore perfectly adaptedfor performing this function. Most preferably, the overlying film has athickness of 5 to 50 nm.

The overlying film is a metallic compound, notably an oxide or nitride,and is preferably of oxide or nitride of titanium, TiO₂ or TiN, or oftantalum oxide Ta₂ O₅. This overlying film has a primary protectivefunction of a mechanical and chemical nature for the functional filmwhich it covers. Depending upon its thickness and also that of thefunctional film, it may also have an interferential role and thuscontribute to the appearance in reflection of the glazing. Its thicknessis at maximum 100 nm, and preferably at least 5 nm. Most preferably, theoverlying film has a thickness of 5 to 50 nm.

The substrate provided with these thin films is therefore suitable foruse either as monolithic glazing or in association with anothersubstrate. It may advantageously be used in building and shipconstruction and in the automobile industry for glazed areas that do notrequire very high values of T_(L).

Referring now to the drawing, FIG. 1 shows one embodiment of the presentinvention. This type of film stack according to this invention notablyenables the objectives of the invention to be achieved: it provides anunderlying film based upon tantalum oxide (2) Ta₂ O₅, preferablyapproximately 100 nm in thickness, a metallic film (3) based upontantalum, adapted notably for achieving a final T_(L) of approximately11%, and an overlying film (4), also based upon Ta₂ O₅, the thickness ofwhich in preferably approximately 14.3 nm.

It should be stated that all these depositions of thin films are carriedout one after the other on the substrate, preferably by the magnetroncathodic sputtering technique in a reactive atmosphere, but that theycould be performed by any deposition technique under vacuum that enablesgood control of the thicknesses of the films deposited to be achieved.

The substrates 1 of silico-sodo-calcic glass, notably float glass, areintroduced by a lock system into the sputtering chamber of thedeposition installation. This sputtering chamber is provided withcathodes having targets of materials corresponding to the deposits to bemade.

The depositions of films 2, 3, 4 are made by successive passes of thesubstrate beneath the metallic target and in appropriate atmospheres.For forming the underlying films 2, the target is of tantalum, titaniumor tin, and the atmosphere is controlled and is composed essentially ofargon and oxygen. For forming the functional films, the target is ofalloy or tantalum and the deposition is performed in an atmosphere ofargon and possibly also nitrogen to form a nitrided film ofnickel-chromium. For forming the overlying film of oxide or of nitride(the present examples relate more especially to an oxide overlyingfilm), a target of titanium or tantalum is used with an atmosphere ofargon/oxygen (or argon/nitrogen in the case of a nitride).

In known manner, the power levels applied to each of the cathodes andalso the speed of travel of the substrate are adjusted in such a way asto obtain the desired thicknesses for the films. The exact thicknessesof the functional film 3 will not, however, be indicated exhaustively inall the examples, insofar as, in a manner well known to the specialistworking on installations for film deposition under vacuum; the objectiveis to control precisely the conditions of deposition, which vary foreach type of installation, in order to achieve very precisely thedesired light transmission, T_(L), without however systematicallydetermining very exactly the thickness of the film which enables thisvalue of T_(L) to be obtained.

Other features of the invention will become apparent in the course ofthe following descriptions of exemplary embodiments which are given forillustration of the invention and are not intended to be limitingthereof.

EXAMPLES

It Should be stated first of all that the external appearance inreflection of the substrate provided with the films according to thisinvention is judged by three values: the value of the external lightreflection on the glass side, R₁ L, given by the configuration of thereflection spectrum in the visible range of said substrate, taking intoaccount the sensitivity of the eye and of a standardized light sourcedesignated by the term illuminant D₆₅, the value of the dominantwavelength, λ_(dom) (R₁ L), in nanometers indicating the colour inreflection, and the purity of excitation pe(R₁ L) indicating the"saturation" of this colour.

The value of the light reflection on the internal side, that is the sidehaving the thin films, is hereinafter designated as R₂ L.

Furthermore, the tests used for assessing the mechanical resistance of astack of thin films according to this invention are now specified:

the abrasion tests enabling the mechanical resistance of the films to beevaluated are performed by means of grinding wheels made of abrasivepowder embedded in an elastomer. The machine in manufactured by thecompany Taber Instrument Corporation of the United States. It is modelnumber 174, "Standard Abrasion Tester", and the grinding wheels are ofthe type CS1OF, loaded at 500 grams. Each specimen is subjected to 300rotations, measure the light transmission at a wavelength of 550 nmbefore (τ₀) and after (τ₃₀₀) abrasion. The abrasion wear is measured bythe value U:

    U%=τ.sub.300-τ.sub.0

The standardized chemical resistance tests carried out are thefollowing:

the tests of resistance to contact with neutral saline mist andcuproacetic saline mist complying with the standard DIN 50021. Theseconsist, notably, of measuring the duration which elapses (in days) upto the time at which the first defect appears in the stack of thinfilms, when this stack is subjected to the standardized atmospherescorresponding to the two the tests.

the test SFW 2,OS for resistance to sulphur dioxide SO₂ complies withthe standard DIN 50018. On the same principle as the two precedingtests, it determines the duration (in cycles of 8 hours exposure andfollowed by 16 hours rest) which elapses until the appearance of analteration which will be specified below.

Examples 1 to 5

The first series of non-limiting examples 1 to 4 concerns a substratehaving thin films possessing a reflection in the visible range on theglass side coloured blue and provided with an underlying film 2 oftantalum oxide and an overlying film 4 of titanium oxide.

The metal target used for obtaining the functional film 3 is of INCONEL671 according to the ASTM standard. Preferably, a sintered target ischosen here, obtained from nickel and chromium powders in theappropriate proportions. In this way, "grains" of sufficiently smalldiameter to obtain a uniform sputtering are obtained.

A homogeneous interdiffusion between the two powders should, moreover,be achieved in order to produce a non-magnetic target.

The substrate 1 is clear float silico-sodo-calcic glass, 6 mm inthickness.

The thickness of the film 3 in each of the examples is chosen in orderto obtain the desired light transmission value, T_(L). In the presentcase, as in the following examples 6 and 7, it lies between 10 and 100nm.

The thicknesses in nanometers of the underlying film 2 of Ta₂ O₅, of thefunctional film 3, of the overlying film 4 of TiO₂, and also the lighttransmission, T_(L), of the assembly comprising substrate/multifilms areindicated below:

    ______________________________________    EXAMPLE  (2) Ta.sub.2 O.sub.5 *                        (3) NiCrN.sub.x *                                   (4) TiO.sub.2                                           T.sub.L    ______________________________________    1        100        15         10      35%    2        100        28         10      19%    3        100        36         10      14%    4        100        45         10       8%    ______________________________________     *nm.

It is found that, by varying the thickness of the functional film 3within the bracket of values previously indicated, it is possible toobtain a wide range of light transmission, T_(L). It should be stated,however, that these thickness values for obtaining a given value ofT_(L) are, in these examples, largely subject to the conditions ofdeposition, and notably to the nitridation level of the alloy deposited.

In order to demonstrate the good performances when subjected tomechanical and chemical corrosions of the substrates coated according tothis invention, a comparison has been made between these four examples,and more especially example 2, and an example 5, composed of a similarstack of three films: metallic oxide/nitrided metallic alloy/metallicoxide, on the same substrate, the characteristics of which are asfollows:

    ______________________________________    underlying film (2)                      mixture of zinc oxide and                      tin oxide, 84 nm thick    film (3)          stainless steel 316 to                      A.I.S.I. standard, 22 nm                      thick    overlying film (4)                      titanium oxide, 10 nm                      thick.    ______________________________________

The photometric characteristics of examples 2 and 5 are close, it beingunderstood that the last column of the following table indicates thecolor in reflection on the substrate side:

    ______________________________________    EX.  T.sub.L                R.sub.1 L                       R.sub.2 L                            T.sub.E                                 λ.sub.dom (R.sub.1 L)*                                         pe (R.sub.1 L)                                                color R.sub.1 L    ______________________________________    2    19%    18%    34%  20%  482     24%    blue    5    20%    17%    43%  17%  480     22%    blue    ______________________________________     *nm.

In both cases, a pastel blue color is obtained in R₁ L. In contrast, thevalue of R₂ L of example 2 is less than that of example 5: thus thecomposite according to example 2, installed as a monolithic glazing in aroom, has a reflection moderated on the side of the thin films (that isto say inside said room if they are on face 2, which enables the"mirror" effect to be limited to the case of weak exterior light andhigh interior luminosity).

In contrast, the corrosion tests on the two coated monolithic substratesgive very different results: (these tests represent the period up to theappearance of an alteration in the stack of films which corresponds to amodification of T_(L) of 10%).

    ______________________________________                    saline   cupro-acetic    EX.     abrasion                    mist*    mist*   sulphur dioxide*    ______________________________________    2       1.8     >62      >50     >37    5       3.7      21       1       >1    ______________________________________     *Time in days until a change of 10% in T.sub.L.

The weakness of the results in the chemical tests of example 5 appear toexclude its use as a monolithic glazing in extreme conditions ofhumidity and/or pollution.

In contrast, the film stack of example 2 according to the presentinvention offers excellent chemical resistance, which demonstrates thesurprising synergistic effect of an underlying film of Ta₂ O₅, anitrided functional film and an overlying film of TiO₂, which enables asubstrate having this type of film stack on face 2 to be used asmonolithic glazing, whatever the conditions of use and/or climaticconditions to which said glazing in normally subjected.

Examples 6 and 7

This second series of examples relates to a substrate, the three thinfilms of which are of exactly the same nature an in the precedingexamples 1 to 4, but it exhibits in reflection, R₁ L, a bronzecoloration for a value of T_(L) of approximately 20%.

The thicknesses of the thin films 2 and 4 according to this inventionare as shown below:

    ______________________________________    EX.   (2) Ta.sub.2 O.sub.5 *                    (4) TiO.sub.2 *                              T.sub.L                                    T.sub.E                                          color (R.sub.1 L)    ______________________________________    6     37.5      10        19%   20%   strong bronze    7     12.5      10        19%   20%   light bronze    ______________________________________     *nm.

Example 8

This time, the substrate is provided with an underlying film 2 of Ta₂O₅, functional film 3 of Ta and an overlying film 4 again Of Ta₂ O₅ :

    ______________________________________    (2) Ta.sub.2 O.sub.5                  underlying film of thickness 100 nm    (3) Ta        functional film for solar protection,                  of thicknesses adapted for obtaining                  a T.sub.L of approximately 11%    (4) Ta.sub.2 O.sub.5                  overlying film of thickness 14.3 nm.    ______________________________________

The photometric characteristics of a film stack of this type are asfollows:

    ______________________________________    EX.  T.sub.L                R.sub.1 L                       R.sub.2 L                            T.sub.E                                 λ.sub.dom (R.sub.1 L)*                                         pe (R.sub.1 L)                                                color R.sub.1 L    ______________________________________    8    11.2%  9.4%   37%  14.5%                                 480     14.6%  blue    ______________________________________     *nm.

Examples 9 to 12

The following series of examples concerns a substrate having thin filmspossessing a reflection in the visible range on the glass side coloredbronze, with an overlying film 4 based upon titanium oxide and anunderlying film 2 also based upon titanium oxide TiO₂.

The metal target used for obtaining the functional film 3 is of INCONEL671 for example 9, that is to say essentially based upon Ni--Craccording to the ASTM standard, produced exactly as described in thepreceding examples 1 to 7.

In example 10, the film (3) also contains iron and the target is ofnitrided steal SST 316 to A.I.S.I. standard.

The substrate 1 is of clear float silico-sodo-calcic glass, 6 mm inthickness.

The thickness of film 3 is adapted in each case in order to obtain thedesired light transmission value, T_(L). In the present case, it liesbetween 10 and 100 nm.

The thicknesses in nanometers of the underlying film 2 of TiO₂, of thefunctional film 3, of the overlying film 4 of TiO₂, and also the lighttransmission, T_(L), of the assembly comprising substrate/multifilms,are indicated below:

    ______________________________________    EXAMPLE  (2) TiO.sub.2 *                       (3) functional film*                                    (4) TiO.sub.2 *                                           T.sub.L    ______________________________________     9       15        28           10     21%    10       15        28           10     21%    ______________________________________     *nm.

In order to demonstrate the good performances of the substrates coatedaccording to the present invention when subjected to mechanical andchemical corrosion, a comparison was made between these two examples,and more especially examples 9 and 10, and an example 11, composed of asimilar stack of 3 films: metallic oxide/nitrided metallicalloy/metallic oxide, on the same substrate, the characteristics ofwhich are as follows:

    ______________________________________    underlying film (2)                     mixture of zinc and tin oxides,                     10 nm in thickness    film (3)         stainless steel 316 to A.I.S.I.                     standard, 20 nm thick    overlying film (4)                     titanium oxide, 10 nm thick.    ______________________________________

The photometric characteristics of examples 9 and 10 on the one hand and11 on the other hand are very close, it being understood that the lastcolumn of the table below indicates the color in reflection of thesubstrate side:

    ______________________________________    EX.  T.sub.L                R.sub.1 L                       R.sub.2 L                            T.sub.E                                 λ.sub.dom (R.sub.1 L)*                                         pe (R,L)                                                color R.sub.1 L    ______________________________________    9    21%    26%    32%  18%  493     2.1%   light                                                bronze    10   21%    25%    30%  17%  504     0.8%   light                                                bronze    11   20%    25%    35%  17%  490     2.1%   light                                                bronze    ______________________________________     *nm

In these three cases, a color in a very pastel bronze tonality isobtained in R₁ L.

The corrosion tests on the three coated monolithic substrates give,however, very different results; (these tests denote the period up tothe appearance of an alteration in the film attack corresponding to theappearance of a first visible defect).

    ______________________________________    EX.   abrasion                  saline mist*                            cupro-acetic mist*                                       sulphur dioxide*    ______________________________________     9    2.5     >78       >90        >20    10    1.5     >78       >90        5    11    2.1      14        1         1    ______________________________________     *time in days until first visible defect appears.

The weakness of the results of the chemical tests of example 11 appearto exclude its use as a monolithic glazing in extreme conditions ofhumidity and/or pollution.

In contrast, the film stacks of examples 9 and 10, and more especiallyof example 9 according to this invention, show excellent chemicalresistance, which demonstrates the surprising synergistic effect of anunderlying film of TiO₂ and of a metal film based upon nitrided nickeland chromium and of an overlying film of TiO₂ ; which once again enablesthe substrate with this type of film stack to be used as a monolithicglazing, whatever the conditions of use and/or climatic conditions towhich said glazing in normally subjected.

In these examples, a small thickness for the underlying film 2 of TiO₂has been chosen, which enables a glazing to be produced, the bronzecolor of which in reflection, R₁ L, is judged fairly favorably inbuilding. It is, however, clear that by varying this thickness; andnotably by increasing it substantially, an interferential effect can beobtained enabling this tonality to be modified. This then makes itpossible to offer glazings having different values of T_(L) and, foreach of these values, different colors in reflection, R₁ L, a selectionof thicknesses which can certainly be readily carried out in all theexamples according to this invention.

Examples 12 to 15

The series of non-limiting examples 12 to 15 concerns a substrate havingthin films possessing a reflection in the visible range on the glassside which are colored blue, with an underlying film 2 of SnO₂ and anoverlying film 4 of TiO₂.

The metallic target used for producing the functional film 3 is ofINCONEL 671 according to the ASTM standard as before.

The substrate 1 is of clear float silico-sodo-calcic glass of 6 mmthickness.

The thickness of the film 3 is adapted in each of the examples in orderto obtain the desired value of T_(L). In the present case, as in thefollowing examples 16 and 17, it lies between 10 and 100 nm.

The thicknesses in nanometers of the underlying film 2 of SnO₂, of thefunctional film 3, of the overlying film 4 of TiO₂, and also the lighttransmission, T_(L), of the assembly comprising substrate/multifilms,are given below:

    ______________________________________    EXAMPLE   (2) SnO.sub.2 *                         (3) NiCrN.sub.x *                                   (4) TiO2*                                            T.sub.L    ______________________________________    12        85 ± 5  15        10       35%    13        85 ± 5  28        10       19%    14        85 ± 5  36        10       14%    15        85 ± 5  45        10        8%    ______________________________________     *nm

In order to demonstrate the good performances of the substrates coatedaccording to this invention, when subjected to mechanical and chemicalcorrosions, a comparison was made between these four examples, and moreespecially example 13, and example 5.

The photometric characteristics of examples 13 and 5 are close, it beingunderstood that the last column of the table below indicates the colorin reflection of the substrate side:

    ______________________________________    EX.  T.sub.L                R.sub.1 L                       R2L  T.sub.E                                 λ.sub.dom (R.sub.1 L)*                                         pe (R.sub.2 L)                                                color R.sub.2 L    ______________________________________    13   19.5%  17.7%  38.6%                            18%  481     25.9%  blue     5     20%    17%    43%                            17%  480     22     blue    ______________________________________     *nm.

In these two cases, a pastel blue colour is obtained in R₁ L. Incontrast, the value of R₂ L of example 13 is less than that of example5.

In contrast, the corrosion tests on the two coated monolithic substratesgive vary different results: (these tests count the period, up to theappearance of an alteration in the film stack which leads to a firstvisible defect).

    ______________________________________    EX.   abrasion                  saline mist*                            cupro-acetic mist*                                       sulphur dioxide*    ______________________________________    13    1.0     >60       >60        >5     5    3.7      7         1         <1    ______________________________________     *Time in days until first visible defect appears.

The weakness of the results in the chemical tests of example 5 is clear.

In contrast, the film stack of example 13 according to this inventionexhibits excellent chemical resistance, which demonstrates thesurprising synergistic effect of a resistant underlying film of SnO₂, ofa nitrided functional film and of an overlying film of TiO₂, whichenables a substrate with this type of multifilm stack to be used as amonolithic glazing pane in face 2, whatever the conditions of use and/orclimatic conditions to which said glazing is normally subjected.

Examples 16 and 17

This series of examples concerns a substrate, the three thin films ofwhich are of exactly the same kind as in the preceding examples 12 to15, but they have in reflection, R₁ L, a bronze coloration with a valueof T_(L) Of approximately 20%.

The thicknesses of the thin films 2 and 4 according to this inventionare as follows:

    ______________________________________    EX.   (2) SnO.sub.2 *                    (4) TiO.sub.2 *                              T.sub.L                                    T.sub.E                                          colour (R.sub.1 L)    ______________________________________    16    30        10        19%   20%   strong bronze    17    10        10        19%   20%   light bronze    ______________________________________     *nm

In conclusion, all the examples of the present application which are inconformity with the present invention relate to glazings which exhibitexcellent corrosion resistance, Furthermore, it in possible to obtainglazings having a large range of spectrophotometric properties.

Thus, by varying the thickness of the functional film, it is possible tochoose the desired light transmission. Furthermore, by modifying onlythe thickness of the underlying film, the range of pastel colors inreflection, R₁ L, can be varied, while maintaining an almost constantvalue of T_(L).

It is self-evident, therefore, that by modifying both the thickness ofthe underlying film and the thickness of the functional film, it ispossible to obtain thin-film substrates of different colors inreflection, R₁ L, and, for each of these colors, different lighttransmissions, T_(L), and energy transmissions, T_(E).

It is also possible to choose a thickness of overlying film of greateror lesser value, in order to classify it as having a protectivefunction, or to give it an interferential function.

It should also be noted that by choosing proper thicknesses for thefilms, it is possible also to modulate the reflection, R₂ L.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A glass composite, comprising:(1) a glasssubstrate; (2) an underlying film of titanium oxide, tin oxide ortantalum oxide; (3) a functional film of tantalum or an alloy ofchromium and nickel; and (4) an overlying film of titanium oxide ortantalum oxide; whereinsaid underlying film (2) is deposited on saidglass substrate (1), said functional film (3) is deposited on saidunderlying film (2), and said overlying film (4) is deposited onfunctional film (3), said films (2), (3), and (4) forming a stack onsaid glass substrate (1).
 2. The glass composite is claim 1, whereinsaid functional film (3) is based on chromium and nickel and isnitrided.
 3. The glass composite of claim 1, wherein said functionalfilm (3) is based upon nickel-chromium in a relative proportion of Ni toCr by mass of about 55/45.
 4. The glass composite claim 1, wherein saidfunctional film (3) contains also iron, and is a stainless steel.
 5. Theglass composite of claim 1, wherein said functional film (3) has athickness of less than 100 nm.
 6. The glass composite of claim 1,wherein said underlying film (2) has a thickness of from 10 to 220 nm.7. The glass composite of claim 1, wherein said film overlying (4) has athickness of from 5 to 100 nm.
 8. The glass composite of claim 1,wherein said substrate (1) is clear float glass with a thickness ofabout 6 mm, said underlying film (2) is tantalum oxide with a thicknessof about 100 nm, said functional film (3) is nitrided NiCr with arelative proportion of Ni to Cr by mass of about 55/45, and saidoverlying film (4) is titanium oxide having a thickness of about 10 nm,and the thickness of said functional film (3) based upon nitrided NiCris adjusted in order that the composite has a light transmission, T_(L),of approximately 19%.
 9. The glass composite of claim 1, wherein saidfunctional film (3) is based on tantalum, said underlying film (2) isbased upon tantalum oxide, and said overlying film (4) also based upontantalum oxide.
 10. The glass composite of claim 9, wherein saidunderlying film (2) has a thickness of approximately 100 nm, and saidoverlying film (4) has a thickness of approximately 14.3 nm, and saidfunctional film (3) has a thickness adjusted in order that the compositehas a light transmission, T_(L), of approximately 11%.
 11. The glasscomposite of claim 1, wherein said substrate (l) is clear float glass ofabout 6 mm thickness, said underlying film (2) is TiO₂ of approximately15 nm in thickness, said functional film (3) is nitrided nickel-chromiumwith a relative proportion of Ni to Cr by mass of about 55/45, saidoverlying film (4) is titanium oxide of approximately 10 nm inthickness, and the thickness of said functional film (3) of nitridedNiCr is adjusted in order that the composite has a light transmission ofapproximately 21%.
 12. The glass composite of claim 1, wherein saidsubstrate (1) is clear float glass of about 6 mm thickness, saidunderlying film (2) is tin oxide of approximately 85 nm in thickness,said functional film (3) is nitrided NiCr in a relative proportion of Nito Cr by mass of about 55/45, said overlying film (4) is titanium oxideof approximately 10 nm in thickness, and the thickness of saidfunctional film (3) of nitrided NiCr is adjusted in order that thecomposite has a light transmission, T_(L), of approximately 19%.
 13. Theglass composite of claim 1, wherein said films that are not purelymetallic are produced by reactive cathodic sputtering under vacuumassisted by a magnetic field, the metallic oxides in the presence ofoxygen, and the nitrided functional films and/or functional films ofnitrides in the presence of nitrogen.